1. Field of the Invention
This invention is related in general to apparatus for aligning two working structures along a desired alignment axis. In particular, it consists of a floating-ball connection for precisely coupling a magnetic head suspension assembly and a testing tool in perfect alignment during the assembly manufacturing process.
2. Description of the Related Art
The magnetic head slider of a magnetic disk system operates by floating in very close proximity over the surface of the magnetic disk, thereby accurately reading and writing data thereon. While the magnetic head slider is floating disposed substantially in parallel over the disk during operation, it must be able to adjust its attitude to conform to magnetic-disk surface imperfections and dynamic displacements, such as surface vibrations generated by the rotating movement. Therefore, the torsional characteristics of the suspension supporting the slider are critical to the proper functioning of the apparatus and must be maintained within prescribed design specifications to prevent contact with the disk surface and avoid the disabling consequences that normally result therefrom.
For illustration, FIG. 1A shows in perspective view a conventional magnetic head gimbal assembly 2 (HGA) positioned over a magnetic disk 4. The head gimbal assembly 2 consists of a slider 6 mounted on a gimbal 8 which is either integral with or rigidly connected to a load beam 10 that comprises a pre-load region 12 and formed rails 22 that provide rigidity to the assembly. The combined gimbal and load beam, which constitute the suspension 11, support the slider portion of the head gimbal assembly. The suspension is in turn attached to a driving mechanism (not shown) by means of a screw or swage mount 14. In operation, the head gimbal assembly 2 is moved by the driving mechanism along the radius of the magnetic disk 4 (arrows A1) so that the slider 6 may be placed rapidly over the appropriate read/write tracks in circumferential direction with respect thereto as the disk is rotated in the direction of arrow A2.
For ease of description, the radial, tangential and vertical directions with respect to the surface of disk 4 are referenced in the figures by x, y and z coordinates, respectively. Thus, the magnetic head slider 6 is supported by the gimbal 8 for controlling pitching and rolling movements as the slider's position changes in the radial (x axis) and circumferential (y axis) directions of the magnetic disk 4. When the magnetic disk is rotated, an air spring is created by the air flowing between the surface of the disk and the rails 16 in the magnetic head slider 6, and the torsional characteristics (roll) of the suspension 11 must be such that the slider maintains its dynamic attitude through surface imperfections and vibrations of the rotating disk.
As magnetic recording technologies evolve, progressive miniaturization of head gimbal assembly components creates critical challenges. One is the tolerance control on the static attitude parameters of the suspension 11 as the slider size is reduced. As the slider 6 becomes smaller, the narrower width between its rails results in smaller differential pressure profiles that produce head gimbal assemblies having flying roll characteristics closely correlated to their static roll attributes. Accordingly, flying attitude characteristics may be predicted well by testing the static attitude of the suspensions under controlled conditions.
Thus, in order to ensure the desired dynamic performance of the suspension (pitch, roll and resonance characteristics), each component of the assembly is manufactured according to specific design specifications and is bench tested for predetermined static parameters. The static attitude of each suspension is measured and compared to allowable tolerances. FIG. 1B illustrates in exploded perspective view the essential portions of conventional prior-art magnetic-head supporting apparatus. The slider 6, to which a magnetic head is mounted (not shown), is attached to a gimbal tongue 42 of the gimbal 8, while the load beam 10 is attached to the outer frame of the gimbal 8 by means of weld points or taps 44. The tongue 42 has a preformed angle and twist and comprises a convex dimple 46 adapted to pivot freely in a concave notch 48 in the load beam 10. Thus, as the magnetic head floats during operation, the dimple 46 pivots freely at the point of contact with the notch 48 in the pitch and roll moments of rotation.
As illustrated in FIG. 2, the static attitude is measured at the mounting surface of the gimbal tongue 42 under load to approximate its flying attitude in the disk drive. The suspension 11 is subjected to a predetermined load at a point along its longitudinal axis and appropriate static measurements are made. Since the components of the suspension consist of very thin stainless-steel structures with extremely low pitch and roll stiffnesses (typically with spring rates in the order of 2 to 10 micro-Joules/degree), a perfect alignment of the axis of the suspension with the testing tool is essential to avoid the introduction of artificial lateral distortions during testing. If the point of contact of the testing tool (that is, the point where the tool pushes against the assembly to impart a load) does not coincide with the suspension's longitudinal axis, a torsional force is introduced that distorts the results. Accordingly, it is very important that such a point of contact with the tool's probe lie on the longitudinal axis of the suspension. This is often difficult to achieve even with very precise instrumentation because of the several components whose cumulative tolerances contribute to the final alignment. Therefore, there exists a need for an improved method of aligning a testing tool with a disk-drive suspension for imparting a test load during the manufacturing process.